Gating system for plan position indicators



June 2, 1953 c. w. sHERwlN GATING SYSTEM FOR PLAN POSITION INDICATORS Filed- April 18, 1946 ATTORNEY `been used for this purpose. .arisen in :operating indicators'in tins manner due Patented June 2, 1953 GATING FORQPLAN .POSITION 4INDICATORS 4'Chalmers W. Sherwin, Leona, N. il., assigner, by

mesne assignments, to the "United States fof America as represented by the :Secretary of Jthe Navy Y Application April "1B, 1946, Serial N0. `662984 fi Claims.

This invention relates to gatingoi fxedcoilpncenterplan position indicators, and more speci'cally -to means for plan-king Tall `but a selected area lof the screen on such fan indicator.

In certain radar vapplications it is kdesirablelto present the Vdata obtained on several :indicators `and Ahave each operator view Vonly a selected `area `of-.the 'total area searched. `,llan 'position Aindicators operated 'with .their 'center displaced lso Vthat `only fa portion of the plot :is ypresented have Diidculties vhave to irregular' .illumination of said indicators when `the electron `beam is deflected `ofi the :tace of the indicator. It is alsonecessary toskno-w'w'hat areas are being searched lloyfeach operator to know that the ,total area jdesired is `,being covered.

It is therefore an object of this invention to provide .a means `of blanking all `'nut a selected `area on a plan position indicator whether it `is operating .normally or oit-center.

.another object of this invention is to `-provide a `means of indicating `on another indicator `the .area that is not blanked on said plan position invdicator.

To .accomplish the yforegoing general objects, .and `more specific objects which hereinafter Aappear, my invention resides in the .circuit 4elements `and their relation Aone to another, as `are vmore :particularly `described. `in the `following specification. The specication is accompanied by a drawing in which:

Fig. l is a diagram illustrating a form of the invention.

The invention Will now be described in `detail vwith .reierenceto Fig. 1 which shows aconventional type `.fixed coil .planposition indicator and associated sweep circuits which have .been modiiied to include .features .of .this invention. The operation of the entire circuit will 'be discussed `with emphasis on the ieaturesfof this invention to provide a .clearer description of its operation.

lvlultivilorator Il is triggered from the radar timer, not shown, and Agenerates.gates of durations corresponding to the maximum ranges used. lvlultivibrator I i in turn triggers sweep generator `and amplifier l2 which develops `a trapezoidal .voltage with a ,duration equal to the gate `from multivibrator i l which trapezoidal voltage is applied to the rotor P5 of rotary transformer l`4. Rotor I5 is turned with scanning antenna i6.

voltages are induced in windings i8 'and 20 'of v.rotary trasnformer lilfrom'th'erotor i5. As the rotor l5 is 'turned with antenna |16 the'voltage in the windings i8 and 20 will also vary "in'proporand 32.

, 2 tion to the position of antenna IB. Resistors 22 and "Eil provide center tapped fground connections to the outputs from windings -IiS and 2. The output from winding i8 -is Aapplied through 4oa- -pactors 2t and 2S to the ygrids of `cathode fiollowers 33 and 32 respectively. Similarly the output from winding 2U is applied through capacitors St `and Elli to the grids `of the remaining. cathode followers 38 and 4D.

Ofi-centering voltages for deiiecting the center horizontally are applied in push `'pull at terminals '42 and dit 'to the lgrids `of cathode followers 3U Similarly off centering voltages lfor/de'- iiecting the center verticalls7 `are applied in push- 'pull 1at terminals 46 and d8 tothe grids of cathode followers 3B and lill. The output from leach cathode follower "30, 32, Stand lll] is taken off from each cathode and 'appliedto therespective grids of driver tubes V5l), 52, 511 and 56. Cathode followers 3i), 32, 38 and 40 serve `'to prevent the flow gridsoi driveritubes 50, 52, 54 and 56,` varyingin amplitude with the position of antenna I6 and Vrotor Ill, *produce linear fsweep Currents in each of the driver tubes 50, 52, 554 and 56 whichvary with the position of antenna I8. These fsweep currents ow through the deflection 'coils 58,66, 62 and 'B4 and deflect 'the indicator electron beam radially in a direction corresponding to `that ci? vantenna I6.

In certain applications it isldesi-red to view'only a selected area around the center of the screen, or in off-center operation it lis desirable to vieW--a small area of the total polar plot at an expanded scale. In off-center operation the electron beam is often displaced ofi the face of the tube inordfr to get thedesiredarea on 'the screen. Whenthe Aelectrons are deflected so tar they often hit-the neck of fthe'cathode rayindicator and are deflected Vonto the screen to produce'undesirable illumidriver tubes will have increased to a point where the voltage drop across its cathode resistor Will bring the voltage, say cathode 12 of driver tube 16 for example, to the voltage level at the cathode of diode 82. Since the plate of diode 82 is tied to cathode 12, when this occurs, diode 82 will conduct. As shown in Fig. 1 cathode 66 of driver tube 50 connects to the plate of diode 88, cathode 68 of driver tube`52 connects to the plate of diode 86, cathode I of driver tube '54 connects to the plate of diode 84, and as explained above cathode 12 of driver tube 56 connects to the plate of diode 82. The cathodes of diodes 82, 84,l 86 and 88 tie in common to point 90. Now whenever the voltage on any cathode 66, 68, or 12 exceeds the `voltage at point 98 the appropriate diode 82, 84, 86 or 88 will conduct and raise the voltage at point 90.

Switch tube 98 obtains its cathode voltage and grid voltage from the voltage divider composed of resistors 92, 94, and 96. The cathode of switch tube 98 receives its potential at variable contact |02 on resistance 94 while the grid of tube 88 |04 on resistor 82. The

mechanically to the one control ||8 so that no -matter what level the grid and thus point 80 are set the cathode voltage will be enough higher to keep switch tube 98 cut-off. Thus the voltage on the plate of tube 88 at point |00 will normally be equal to the applied voltage E+. This isapplied to -control grid 9 to bias the electron beam of indicator tube I0 to conduction under normal conditions when vthe electron beam is on the face of indicator I0. Whenever the electron beam moves to one side of the indicator I8 one of the diodes 82, 84, 86 or 88 will conduct and bring the voltage of point 98 and thus grid ||4 up to make switch tube 98 conduct. (Resistor |08 serves to protect grid H4 when grid current flows.) This will cause the voltage at point |00 and terminal I |2 to drop and the signal being fed to indicator` |8 will bias the electron beam to cut-ofi' so it cannot reect oiT the neck of the tube to produce undesired illumination on the screen. Thus it mayl .be seenv that as long as the electron beam is directly on the selected area of the screen on indicator l0 switch tube 98 will be cut-oir and the indicator |0 will be unblanked but when the electron beam goes outside the area on the face of the indicator tube 98 will conduct and supply a blanking pulse to the indicator I0 at terminal I2. The size of the square area presented on indicator I8 may be varied by changing the voltage level at point 98 by means of control ||0.

Switch tube ||6 receives a gate from multivibrator which is coupled through capacitor |8 to the grid of the tube I6. This gate causes tube ||8 to cond-uctduring the ily-back time of each sweep on indicator I0 and prevents the trace .from appearing on indicator l0 during fly-back time,

' be equal to E`| while switch tube 98 is cut-oir during a sweep but while the sweep is in the area presented on indicator |0 this voltage will be reduced. This voltage may then be used to intensify by biasing to conduction the cathode ray tube of, another indicator |0A, the area. which is being viewed on indicator I0 thus another operator can tell what area is being covered by indicator I0.

It is believed that the construction and operation as well 'as the advantages of my improved indicator gating circuit will be apparent from the foregoing detailed description thereof. It will also be apparent that while I have shown and described my invention in a preferred form changes may be made in the circuit disclosed without departing from the spirit of the invention as sought to be defined in the following claims.

What is claimed is:

l. In a radar system employing xed coil type l plan position indicators, a first cathode ray tube,

means for sweeping the screen of said rst cathode ray tube with an electron beam for presenting radar data on said screen, means for offcentering the origin of the sweep of said rst cathode ray tub-e to present a selected area on said screen, a second cathode ray tube, means for sweeping the screen of said second cathode ray tube with an electron beam for presenting radar data on said screen, means for positioning the origin of said last mentioned sweep substantially at the center of said second cathode ray tube, means for intensifying said electron beam in said rst cathode ray tube during the time of directly striking the screen thereof, said means being operative to provide an output applicable with radar data to said second cathode ray tube, thereby producing a bright area on the screen of said second cathode ray tube, indicating the area presented on said iirst cathode ray tube.

2. In a plan position indicator employing a cathode ray tube with fixed deilection coils and four driver tubes, means including said driver tubes for sweeping the screen of said cathode ray tube with an electron beam, means for presenting radar data, on the screen of said tube, means for offcentering the origin of said sweep to present a selected area on said screen, means employing separate diodes responsive to each of the Ioutputs of said driver tubes for determining the deflection of said electron beam in any direction from the center of said screen, means employing a rst switch tube for blanking said electron beam of said cathode ray tube Whenever said electron beam is deflected a predetermined distance in any direction, means employing a second switch tube to blank out said cathode ray tube during the period between sweeps and during the iiy back time of each sweep, and means 'employing a potentiometel` for adjusting the distance said electron beam may travel across said 'screen from the center oi said cathode ray tube Elo adjust the area of said rad-ar data presenta- 3. In a cathode ray tube having a fixed coil type deflection system, means for energizing said deflection system to cause the beam `of said tube to trace a predetermined scanning pattern. means to shift the center of said scanning pattern off the center of the screen of said tube to present a selected area of said pattern on said screen, a normally nonconducting switch tube for biasing said cathode ray tube and means responsive to the current ow in said deflection system for biasing said switch tube to conduction thereby biasing said cathode ray tube to nonconduction whenever said currents dellect said beam on' said screen.

4. A circuit for` controlling the intensity of the beam of ya cathode ray tube having a` fixed coil type deflection system comprising, means biasing said cathode ray tube to be normally conducting, means for energizing said deflection system to cause said beam to trace a predetermined scanning pattern, means for off centering the origin of said scanning pattern on said screen to present a selected areaq of said pattern, a switch tube biased tol be normally nonconducting and connected upon conduction to bias said cathode ray tube to nonconduction, and means responsive to the current flow in said deflection system to bias said switch tube to conduction for current amplitudes deieoting said beam off said screen,

CHALMERS W. SHERWIN.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,400,791 Tolson May 2l, 1946 2,401,432 Luck July 4, 1946 2,409,456 Tolson Oct. 15, 1946 2,421,747 Englehardt June 10, 1947 2,531,466 Ranger Nov. 28, 1950 

